1. Field of the Invention
The present invention relates to a communication control device and a communication control method in an audio visual device system, and a television receiver.
2. Description of the Related Art
In HDMI (High-Definition Multimedia Interface), since it is possible to recognize devices connected to each other, the devices can be controlled and caused to cooperate with each other in addition to that video and audio signals can be transferred through a cable. Data transmission/reception and communication (refer to “High-Definition Multimedia Interface Specification 1.3a”) of a system in which a television receiver (TV receiver) is connected to recording devices such as a hard disc recorder through HDMI will be explained using a block diagram of FIG. 13 and a timing chart of FIG. 14.
First, a procedure for recording devices 902, 903 to acquire physical addresses will be explained. When the recording devices 902 and 903 set 5V PWR (+5V power supply) lines to high, the TV receiver 901 sets an HPD (Hot-Plug Detect) line to high. It is found that the recording devices 902, 903 can perform a DDC (Display Data Channel) communication by these operations. Thereafter, the recording device 902 or 903 acquires a physical address from an EDID (Extended Display Information Data)-ROM (not shown) of the TV receiver 901 by a DDC communication. DDC is a standard determined by VESA (Video Electronics Standards Association) to transmit information as to display stored in the EDID-ROM to a display data transmission side by communication. Here, the physical address of the TV receiver 901 is fixed to 0.0.0.0. The physical addresses of the recording devices 902 and 903 are prescribed in the EDID-ROMs connected to respective HDMI ports of the TV receiver 901 and are set to, for example, 1.0.0.0 and 2.0.0.0.
Subsequently, when the TV receiver 901 switches an input and selects the recording device 902 as an external input, the recording device 902 communicates with HDCP-ROM of the TV receiver 901 by the DDC communication. With this operation, an authentication process as to copyright protection is performed, and a cipher key is provided. Thereafter, the recording device 902 can transmit image data and audio data to the TV receiver 901.
Next, a method of acquiring a logical address will be explained. Logical addresses which can be acquired are previously determined for each of device types (refer to FIG. 15). For example, the logical addresses of the recording devices are set to any of “1”, “2”, “9”. Accordingly, the number of logical addresses of each device type has an upper limit allocated thereto. The recording device 902 transmits, by broadcast, a Polling message to a logical address (for example, “1”) the acquisition of which is desired by the recording device 902. When no response to the message returns from any device (when a message returns in the state of ACK bit=1), it can be found that the logical address is available, and the recording device 902 acquires the logical address. When a response returns (when a message of ACK bit=0 returns), on the other hand, the logical address is already acquired by other device. In this case, a logical address is acquired by repeating the same process to other logical addresses (for example, “2” and “9”) (refer to, for example, Japanese Patent Application Laid-Open Publication No. 2007-202115 and “High-Definition Multimedia Interface Specification, Version 1.3a, P. 194-197”). FIG. 14 shows timings at which the processes described above are performed. In FIG. 14, a horizontal axis shows a time, and a vertical axis shows how the processes are time-sequentially performed from left to right.